Which methods are idempotent

However, the See Other response can be used to direct the user agent to retrieve a cacheable resource. If the Request-URI does not point to an existing resource, and that URI is capable of being defined as a new resource by the requesting user agent, the origin server can create the resource with that URI.

If a new resource is created, the origin server MUST inform the user agent via the Created response. Responses to this method are not cacheable. That resource might be a data-accepting process, a gateway to some other protocol, or a separate entity that accepts annotations. If the server desires that the request be applied to a different URI,. For example, an article might have a URI for identifying "the current version" which is separate from the URI identifying each particular version.

This method MAY be overridden by human intervention or other means on the origin server. The client cannot be guaranteed that the operation has been carried out, even if the status code returned from the origin server indicates that the action has been completed successfully.

A successful response SHOULD be OK if the response includes an entity describing the status, Accepted if the action has not yet been enacted, or No Content if the action has been enacted but the response does not include an entity. The final recipient is either the. Request methods are considered "safe" if their defined semantics are essentially read-only ; i.

This definition of safe methods does not prevent an implementation from including behavior that is potentially harmful, that is not entirely read-only, or that causes side effects while invoking a safe method. What is important, however, is that the client did not request that additional behavior and cannot be held accountable for it.

Idempotent Methods. A request method is considered "idempotent" if the intended effect on the server of multiple identical requests with that method is the same as the effect for a single such request.

Like the definition of safe, the idempotent property only applies to what has been requested by the user; a server is free to log each request separately, retain a revision control history, or implement other non-idempotent side effects for each idempotent request. Summarizing, the HTTP methods are classified as following :. However, to prevent collisions, PATCH requests can be issued such a way as to be idempotent, as quoted below:. A PATCH request can be issued in such a way as to be idempotent, which also helps prevent bad outcomes from collisions between two PATCH requests on the same resource in a similar time frame.

Collisions from multiple PATCH requests may be more dangerous than PUT collisions because some patch formats need to operate from a known base-point or else they will corrupt the resource.

Clients using this kind of patch application SHOULD use a conditional request such that the request will fail if the resource has been updated since the client last accessed the resource. After each request the server-state is the same, therefore idempotency is fulfilled.

It would not matter if the method is called only once, or ten times over. The result should be the same. It essentially means that the result of a successfully performed request is independent of the number of times it is executed. For example, in arithmetic, adding zero to a number is idempotent operation. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Consider the situation where you are integrating your system with an external one which is quite typical with REST isn't it:- and you want to provide reliability ie. In this case idempotence might be your friend since you can retry the failed operation as many times as you want.

Well the order of execution could matter ie. An idempotent operation is not always readonly, it only ensure that if the operation is called twice with the same parameters the post-condition is unaffected Bingo. That right there summarizes what "service" idempotency means to me. It should only matter if its post-conditions hold.

The entire set of valid and validated requirements will dictate what idempotency is and what services will meet that criteria and perhaps by how much if the requirements call for a idempotency gradient. IMHO idempotence is a matter of 'common sense'. For instance, the expected result of various calls to update a registry, if it has the same input values, the user expect to have the same result. If the inputs are different, the expected result will be different… You may not search for idempotence, but you found it in some calls.

The HTTP spec if quite helpful www. These methods ought to be considered "safe". The important distinction here is that the user did not request the side-effects, so therefore cannot be held accountable for them. If logging does not affect the user say it is only used for auditing and diagnostics then performing logging within a GET request for a resource does not stop it being idempotent.

As an example, if a GET request had a side-effect like erasing some of the user's data or another user's data or sending something to a printer, then that would break idempotence and would matter. Like Print Bookmarks. Apr 28, 4 min read by Mark Little.

An idempotent method means that the result of a successful performed request is independent of the number of times it is executed. The inital post starts with: Currently I am looking at Idempotency of our services and coming up with a prescriptive guide for the enterprise in creating cases you create idempotent services.

The question is do does all services need to be idempotent? Is it realistic? It references another blog entry , where that author makes the following assertions: Of course, implementing idempotency can be complex for the service provider.

And complexity costs money. That's probably the real reason why idempotent services are so rare. Services should be made idempotent. It should be an architectural and service design principle. Especially so for services which are used by many service consumers. You can't really push out your own complexity of keeping data consistent to your consumers, can you? Why String is Immutable in Java?

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